As described in Japanese Patent Application Laid-Open (kokai) No. 2012-18050, there is known a gas sensor capable of detecting the concentration of a particular gas contained in a gas under measurement by heating the gas sensor to a predetermined activation temperature or higher. Such a gas sensor has a heater for bringing the gas sensor into a condition capable of detecting a particular-gas concentration (i.e., an activated condition) at an early stage after start-up.
The internal resistance of a detection element formed by use of a solid electrolyte body has a characteristic of changing in correlation with the temperature of the detection element. Thus, a sensor control apparatus for controlling the detection element detects the internal resistance and drives the heater on the basis of a temperature calculated by use of the detected internal resistance, thereby heating the detection element to a target temperature.